Many high molecular weight polysaccharides can be produced by biological reactions, see for example U.S. Pat. No 4,230,699, which relates to the preparation of a natural heteropolysaccharide and U.S. Pat. No 4,329,448, which relates to a novel heteropolysaccharide known as Biopolymer PS 87.
It will be apparent from these specifications and other art that such reactions produce the desired polysaccharide in a dilute concentration. Proposals have been made in the prior art to separate out the polysaccharide from the aqueous medium by, for example, the addition of a large quantity of a water-miscible alcohol which precipitates out the polysaccharide. Other proposals for separation require additional steps to the use of a water-miscible solvent such as those described in U.S. Pat. No 4,230,699, in which the precipitate is solubilised in a solution of a strong mineral acid, then treated with a quaternary ammonium halide and further treated with a water-soluble salt.
These prior art processes have various disadvantages, for example, some require large amounts of energy if the water-miscible solvent is to be separated from the bulk of the aqueous residue after removal of the polysaccharide and the present invention discloses a process which is far less extravagant in the use of energy and can, in a preferred form, involve recycling of the component chemicals involved in the process.
This invention is based on the discovery that by adapting certain multiphase systems, aqueous solutions containing polysaccharides can be caused to throw out the polysaccharide in a form in which it can be readily separated from the aqueous mixture.
In the book "Advances in Liquid Crystals", Vol I, edited by Glenn H. Brown and published by Academic Press in New York in 1975, phase diagrams are considered for various systems including water, fatty acid salts and alcohols.
The zones of compatibility are discussed and referred to in the phase diagrams by the letter L. In some cases the zones are split by other areas having different physical properties and the compatible zones are then indicated by L.sub.1 and L.sub.2.